Here are a list of featured diagrams, showing the kind of things you can do with GitUML.
Since May 2020, GitUML has the capability to reverse engineer Objective C.
Here are some diagrams featuring the DZNEmptyDataSet repository on GitHub.
These are diagrams from the GitHub repository of one of my other projects, Pynsource, a desktop UML app for Python.
This project has been going for 10+ years and is open source. It actually led to the creation of GitUML and shares parts of its Python parser.